NURBS-based mixed triangular-quadrilateral meshes and Kirchhoff approximation method for acoustic scattering analysis of underwater targets

This paper introduces a novel computational framework for the efficient simulation of high-frequency acoustic scattering from underwater targets. The framework utilizes NURBS-based geometry representation and mixed triangular-quadrilateral mesh generation, enabling automated and parameterized discretization of complex surfaces. By integrating the Kirchhoff approximation with the planar element method (PEM), the model facilitates rapid prediction of target strength over a wide frequency range. Validation studies on simple geometries, such as a rigid sphere and a prolate spheroid, demonstrate excellent agreement with analytical solutions. Furthermore, the method is applied to realistic submarine models (the BeTSSi model 3 and a scaled BeTSSi model), highlighting its ability to handle geometrically intricate targets. The accuracy of the BeTSSi model 3 is validated against other numerical methods, while the scaled BeTSSi model is verified through experimental testing. These results indicate that the proposed framework achieves high computational efficiency and accuracy, making it well-suited for target characterization and classification in underwater acoustic applications.